Lately I've been working up some loads for my .223 AI. My goal is 3800 fps with a 40 grain Sierra BlitzKing.
For the record, I'm using a calibrated and zeroed RCBS 1500 Chargemaster Combo with Redding Type S Match Neck Sizing dies.
The load:
Sierra BlitzKing 40 grain
Hodgdon H322
Fully prepared R-P brass fireformed to the AI dimensions in my gun
Federal Gold Medal Match Small Rifle primers
I originally worked up this load back in October 2005.
8 Oct 05 (temp 80) 27.0 grains. OAL 2.905" Average velocity over 10 shots 3792.9 fps. I thought to myself, "Velocity is about right, but the low end was a bit lower than I wanted (3720 fps). I'll bump it up .2 and see where I end up."
9 OCT 05 (temp 80) 27.2 grains. OAL 2.905" Average velocity over 10 shots 3842.2 fps. Ahh..much better!
After some experimentation with OAL, I learned that my gun preferred the bullets seated long. I now seat them to 2.955" versus 2.905".
After altering the OAL, I chronographed again.
30 Mar 06 (temp 60) 27.0 grains. OAL 2.955" Average velocity over 10 shots 3660.1. Difference of 132.0 fps.
30 Mar 06 (temp 60) 27.2 grains. OAL 2.955" Average velocity over 10 shots 3699.4. Difference of 142.8 fps.
It was at this point that I began to get curious about what load would provide 3800 fps again. I loaded up several loads (27.0, 27.1, 27.2, 27.3) to see where I stood. Velocity over the four loads varied from 3660 to barely over 3700 fps. I was dismayed at the required change in charge weights. The next weekend, I did the same thing with four more loads (27.4, 27.5, 27.6, 27.7). Again I was disappointed although I was getting closer. The next day I went back....determined to get to 3800 fps. This time I had loaded 27.8, 27.9, 28.0 and 28.1 grains. The largest amount of propellant (28.1) had finally provided an average of 3800.2! I was there!
I found it very interesting that such a small change in OAL (and the resulting case capacity) and temperature makes such a big difference (especially on a claimed temperature insensitive propellant) on velocity.
FYI, here's a chart depicting all the changes throughout the loading progression. By the way, take a look at the 28.2 load. I find the ES and MAD very interesting. While not listed, the SD was 55.3 fps for 1.43% of the whole velocity. I'm assuming I'm getting into dangerous pressure. No other signs of pressure were observed though.
Enjoy,
Ed
For the record, I'm using a calibrated and zeroed RCBS 1500 Chargemaster Combo with Redding Type S Match Neck Sizing dies.
The load:
Sierra BlitzKing 40 grain
Hodgdon H322
Fully prepared R-P brass fireformed to the AI dimensions in my gun
Federal Gold Medal Match Small Rifle primers
I originally worked up this load back in October 2005.
8 Oct 05 (temp 80) 27.0 grains. OAL 2.905" Average velocity over 10 shots 3792.9 fps. I thought to myself, "Velocity is about right, but the low end was a bit lower than I wanted (3720 fps). I'll bump it up .2 and see where I end up."
9 OCT 05 (temp 80) 27.2 grains. OAL 2.905" Average velocity over 10 shots 3842.2 fps. Ahh..much better!
After some experimentation with OAL, I learned that my gun preferred the bullets seated long. I now seat them to 2.955" versus 2.905".
After altering the OAL, I chronographed again.
30 Mar 06 (temp 60) 27.0 grains. OAL 2.955" Average velocity over 10 shots 3660.1. Difference of 132.0 fps.
30 Mar 06 (temp 60) 27.2 grains. OAL 2.955" Average velocity over 10 shots 3699.4. Difference of 142.8 fps.
It was at this point that I began to get curious about what load would provide 3800 fps again. I loaded up several loads (27.0, 27.1, 27.2, 27.3) to see where I stood. Velocity over the four loads varied from 3660 to barely over 3700 fps. I was dismayed at the required change in charge weights. The next weekend, I did the same thing with four more loads (27.4, 27.5, 27.6, 27.7). Again I was disappointed although I was getting closer. The next day I went back....determined to get to 3800 fps. This time I had loaded 27.8, 27.9, 28.0 and 28.1 grains. The largest amount of propellant (28.1) had finally provided an average of 3800.2! I was there!
I found it very interesting that such a small change in OAL (and the resulting case capacity) and temperature makes such a big difference (especially on a claimed temperature insensitive propellant) on velocity.
FYI, here's a chart depicting all the changes throughout the loading progression. By the way, take a look at the 28.2 load. I find the ES and MAD very interesting. While not listed, the SD was 55.3 fps for 1.43% of the whole velocity. I'm assuming I'm getting into dangerous pressure. No other signs of pressure were observed though.
Enjoy,
Ed
